Crude oil is a complex mixture of various paraffinic and aromatic hydrocarbons in which the individual constituents have very different chemical and physical properties. Accordingly both readily volatile, low-viscosity constituents and wax-like, high-viscosity fractions are obtained in the distillation of crude oil. The second of these two groups includes petroleum resins and, to a predominant extent, asphaltenes which are colloidally dispersed in the oil phase.
The asphaltenes consist of a mixture of various saturated, unsaturated and aromatic hydrocarbons, more particularly naphthalene derivatives. Besides these, there are also found heterocyclic hydrocarbons which, in part, also contain complexed metal ions. In addition, asphaltenes are rich in sulfur, nitrogen and oxygen compounds. Because of their complex composition, asphaltenes are generally characterized on the basis of their solubility. Thus, the petroleum fraction insoluble in heptane or pentane, but soluble in toluene is referred to as asphaltenes, the “dissolution” of asphaltenes involving a complex process for which there has as yet been no complete theoretical explanation (cf. E. Y. Sheu, O. C. Mullins, Asphaltenes—Fundamentals and Applications, Plenum Press, New York, 1995,Chapter I and Chapter III).
Asphaltenes are present as micelle colloids in the oil phase of crude oil, the individual micelles consisting of several different molecules. The micelles vary in size according to the temperature and composition of the oil phase. For example, it is known that relatively light aromatic hydrocarbons in crude oil stabilize the asphaltene micelles. Under the conditions prevailing in petroleum production or recovery, however, the asphaltenes are often precipitated, which results in the formation of highly viscous, wax-like or solid residues on the surface of the production units and the petroleum-containing formation surrounding the well. The asphaltene residues block the pores of the formation, which leads to a noticeable reduction in the production rates and, in the worst case, can make production completely impossible. Asphaltene residues on the surfaces of the production units, for example the delivery tube or the casing walls of pipelines or separators, can also considerably reduce production.
Accordingly, there are various known methods for keeping asphaltenes dispersed in crude oil and for preventing their precipitation. In this regard, DE 197 09 797 describes synergistic mixtures of alkylphenol-formaldehyde resins and certain alkoxylated amines as asphaltene dispersants. It is known from U.S. Pat. No. 4,414,035 that alkylarylsulfonic acid derivatives, for example dodecylbenzenesulfonic acid, are suitable for dispersing asphaltenes in crude oils.
However, it has often been found in practice that known auxiliaries for stabilizing asphaltenes differ very considerably in their effectiveness according to the nature and origin of the crude oil. This is attributable in particular to the complex and highly variable structure of the asphaltenes. Accordingly, efforts have been made to find new asphaltene stabilizers. In addition, asphaltene stabilizers known in the prior art are often either toxic and/or ecologically unsafe. Both for reasons of environmental compatibility of operating media and in the interests of safety at work, attempts are therefore being made to avoid using such substances.
Accordingly, the problem addressed by the present invention was to provide effective alternatives to the stabilizers known from the prior art for stabilizing asphaltenes in crude oils, even for very different crude oil grades. It has been found that certain polyester amides solve this problem.